Starting-rheostat.



@ PATENTED JUNE 2, 1903.-

C. E. HARTHAN.

STARTING RHEOSTAT.

APPLICATION FILED MAB. a. 1902.

3 SHEETS-SHEET 1 E0 MODEL.

lndeniioru C ha le s ELHaP chan PATENTED JUNE 2, 1903.

G. E. HARTHAN.

STARTING RHEOSTAT.

APPLICATION FILED MAB. 8, 1902.

3 SHEBTS-SHEBT 2.

I0 KODEL.

I lno'en corw Ch SPIGS BrHavb'han,

W'tnessesz Q l No. 729,762. PATENTED JUNE 2 1903.

0. E. HARTHAN.

STARTING RHEOSTAT- APPLIOATION FILED MAB. 8, 1902.

N0 MODEL. 3 BHEET8-SHEBT 3.

Fig.5.

witnesses: InOe'nbor,

, 75 Charles El+-|er-than y I v q tj UNITED STATES Patented June 2, 1903.

PATENT OFFICE.

CHARLES E. HARTHAN, OF LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

STARTING-RHEOSTAT.

SPECIFICATION formingpart of Letters Patent No. 729,762, dated June 2, 1903.

Application filed March 8, 1902. Serial No. 97,322 (No model.)

To whom it may concern:

Be it known that I, CHARLES E. HARTHAN, a citizen of the United States, residing at Lynn, county of Essex, State of Massachusetts, have invented certain new and useful Improvements in Starting-Rheostats, of which the following is a specification.

This invention relates to switches for con trolling the circuits of electric motors and other electrodynamic apparatus, such as starting-rheostats, circuitbrcakers, and the like; and its object is to provide means for automatically opening the circuit on an overload. The usual apparatus for accomplishing this result includes an electromagnet adjusted to actuate its armature when the current becomes excessive, and thus short-circuit the electromagnet which retains the arm of the starting-rheostat or the main contact of the circuit-breaker in the on position, thereby permitting a spring to return said arm or contact to the off position. The overload electromagnet acts the instant the predetermined excess of current occurs, which under some circumstances is objectionable, since a momentary flow of excessive current is often not injurioussuch, for instance, as happens when starting a motor or throwing on heavy loads.

My invention provides an overload device which does not operate instantly, but only after an interval of a minute or two.

It consists of a thermostat in series with the line, so that it will be heated by the current. \Vith an excessive flow the thermostat becomes sufficiently hot to close a pair of contacts, and thereby short-circuit the retainingmagnet and permit the spring to throw off the rheostat or circuit-breaker, and thereby open the circuit. This operation occupies between one and two minutes; but when the current is cut off the thermostat quickly cools and opens the short-circuiting contacts.

The device can be made. to operate at any 5 desirable range of current or degree of overload.

In the accompanying drawings, Figure 1 is a front elevation of a starting-rheostat embodying my invention. Fig. 2 is a top plan view of the thermostat on a larger scale. Fig.

3 is an end view of the same. Fig. l is a diagram of the circuits, and Fig. 5 shows the invention applied to a circuit-breaker.

Referring to Figs. 1, 2, 3, and 4, at A is shown the armature and at B the field-coil of a shunt-wound motor, whose circuit 1 1 is opened and closed by a double-pole switch C and controlled by a rheostat D. The arm (I. of the rhcostat makes contact with the steps (1, thereby successively cutting out the resist- 6o ance-coils (Z from the armattire-circuit 2 2. An electromagnet d in the field-coil circuit 3 3 retains the arm in position when all the rcsistance has been cut out. When a shunt-circuit at 4 is closed around this magnet, a spring d" returns the arm d to the off position, as shown in Figs. 1 and 4:, opening the armature-circuit, and so stopping the motor. These parts are all old and in common use. My invention lies in the device which I employ in this combination for closing the shunt 4 4 and short-circuiting the retaining-magnet d.

In the shunt is included a pair of contacts, normally separated so as to keep the shunt open. Insteadof a magnet for closing these contacts I provide a thermostatic circuitcloser so arranged that its temperature will vary with the current. At a predetermined degree of heat the thermostat closes the contacts.

Various forms of thermostats may be e1nployed in this connection. I prefer the one shown in the drawings, consisting of two arms E, each composed of two metals having dissimilar coeificients of expansion and contrac- 8 5 tion. These arms I put in series with the armature, attaching them at one end to stationaryclips E and connecting them elec= trically by a leaf-springE At their free ends they carry the contacts F, one or both 0 of which maybe adjustable. These contacts are insulated from thearms, preferably by being mounted in laterally-projecting fingers G, secured to the arms by screws g, but insu lated therefrom by interposed insulation H. 5

In case of an overload the arms on becoming heated close the contacts F and shunt the magnet (Z thereby allowing the spring cl to open-circuit the armature of the motor.

Fig. 5 shows a circuit-breaker equipped 10o with my invention and in circuit with a gen.- erator and a trolley-car. The fixed contacts I, the movable bridging-contact K, the blowout coils L, the toggle M, with its handle M, and the circuit-opening spring N are all of any usual construction. In place of the customary overload-magnet I employ a magnet I which holds the toggle locked so long as current flows through it. My thermostatic overload device is arranged so that an excessive flow of current will heat the thermostat to a point where it will close the shunt, thereby denergizins, the magnet P and tripping the circuit-breaker.

My invention is not necessarily limited to the exact construction shown in the drawings, but may be varied in many ways without departing from the spirit or scope thereof.

WVhat I claim as new, and desire to secure by Letters Patent of the United States, is-

1. The combination with a switch having a retaining-magnet, of a thermostat whose temperature varies with the current, and a shunt around said magnet controlled by said thermostat.

2. The combination with a switch having a retaining-magnet, of a thermostat in series with the switch, and a shunt around said ma g= net controlled by said thermostat.

3. The combination with a switch having a retaining-magnet, of a thermostatic arm in series with the switch, a contact on said arm, and a shunt around said magnet including said contact.

4. The combination with a switch having a retaining-magnet, of two connected thermostatic arms in series with the switch, and iiisulated contacts carried by said arms and included in a shunt around said magnet.

5. The combination with a switch having a retaining-magnet, of two thermostatic arms fastened at one end, a leaf-spring connecting said arms, an insulated finger at the free end of each arm, and a contact carried by said finger and included in a shunt around said magnet.

In witness whereof I have hereunto set my hand this 6th day of March, 1902.

CHARLES E. HARTHAN.

Witnesses:

DUGALD McKILLoP, JOHN McM NUs. 

